Generally, for in-country case, radioactive waste was firm-processed with cement, but was suspended due to increase of volume that originated from large quantity of firming material. Afterwards, paraffin firm-processing is being done, but paraffin firming agent is difficult to satisfy acceptable criteria for radioactive waste disposal area.
In case of US, research on developing procedures using ceramic low-temperature melting furnace is being performed to vitrify nuclear power plant originated radioactive wastes. In terms of hardening radioactive wastes using cement, there have been occurrences of weaknesses such as iron corrosion and wastewater following the long-term storage in Westinghouse, US, ORNL (Oak Ridge National Laboratory), Hitachi, Japan, and INER (Institute of Nuclear Energy Research), Taiwan, and in terms of polymer solidification, reconsideration of polymer degradation reaction on high-dose radioactive waste in DTS (Diversified Technologies Services Company), US, and Grenoble Nuclear Power Plant, France.
Therefore application of vitrification, which improved the weakness of previous hardening methods on radioactive wastes while having excellent processing effect and eco-friendliness, was considered.
Meanwhile, pelletizing method, granulation method and injection method are being suggested for pre-processing the radioactive waste, and the results following were shown as Table 1.
TABLE 1Comparative analysis on pre-processing methodPre-In-processingFinal stallation Maint-Operationmethodproduct conditionenanceconvenienceWashingPelletizingGoodGoodGoodGoodUn-methodnecessaryGranulationIn-AverageAverageAverageNecessarymethodappropriateInjectionIn-AverageDifficultDifficultNecessarymethodappropriate
Pelletizing method is in general a method of producing medication tablets, and can be separated into method of manufacturing by mixing powder with additive (binder, excipient, lubricant, disintegrating agent) and granulating (wet assembly, dry assembly), and method of manufacturing by adding force directly into powder after mixing the powder with additive without granulation process. Additives are used to improve hardness and friability, and various additives such as PVA (Polyvinyl alcohol), HPMC (Hydroxypropyl methylcellulose), HPC (Hydroxypropylcellulose), Kollidon VA 64 are used.
FIG. 1 is a method of making radioactive waste powder into tablets, which is a method of pre-processing radioactive waste following the conventional art, and is a procedure flow chart that shows tablet formulation method of radioactive waste powder which was previously applied as Registered Patent No. 10-0933561.
Referred to FIG. 1, an apparatus for tabletizing radioactive waste is formed with mixer (A), powder molding press (B), and coating apparatus (C). The radioactive waste is mixed with binder and lubricant in mixer (A), made into tablets with powder molding press (B), and is formed with coating in coating apparatus (C).
However, the conventional apparatus for tabletizing radioactive waste is formed with mixer (A), powder molding press (B), and coating apparatus (C), so it is difficult to be applied when considering the small installation space of nuclear power plant. Also, the tablet manufacture method of the prior art has weakness of complex procedures, and it requires drying apparatus to maintain the moisture level of radioactive waste lower than 0.5%. Also, various additives (binder, lubricant, coating agent) are used, so handling and mixing procedures are complicated, and standard of tablet, which is the most basic item when applied to a vitrification facility, is not provided. Moreover, radioactive waste has potential of pollute expansion via dispersing as small particles, which requires pollution spread preventing apparatus, but such apparatus did not exist before.
Also, when vitrifying radioactive waste, glass composition developing procedure is needed to develop the needed glass composition. Radioactive waste vitrification is different from general industries' vitrification, by having enough standards to prevent radiation-emitting radioactive wastes from leaking into environments by locking up in glass structure, and such standard must not be problematic when applied to a vitrification facility.